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Diversions, marsh vertical accretion, and soil strength J . Andy Nyman

Diversions, marsh vertical accretion, and soil strength J . Andy Nyman School of Renewable Natural Resources LSU AgCenter and LSU jnyman@lsu.edu. Diversions sediment diversions freshwater diversions vertical accretion belowground biomass production soil strength. conclusions.

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Diversions, marsh vertical accretion, and soil strength J . Andy Nyman

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  1. Diversions, marsh vertical accretion, and soil strength J. Andy Nyman School of Renewable Natural Resources LSU AgCenter and LSU jnyman@lsu.edu

  2. Diversions • sediment diversions • freshwater diversions • vertical accretion • belowground biomass production • soil strength

  3. conclusions • marsh vertical accretion depends directly upon organic matter accumulation (and probably indirectly upon mineral sedimentation) • soil strength depends directly upon live roots (and probably indirectly upon mineral sedimentation) • marshes receiving more river water have greater aboveground production, no difference in belowground production, and no difference in soil organic matter decomposition than those receiving less river water

  4. DeLaune et al. 1990. Catena 17:277-288

  5. Blum et al. 2008. Geology 36:675-678

  6. 9.8 mm/yr 7.4 mm/yr Nyman et al. 2006 Estuarine Coastal and Shelf Sci 69:370-380

  7. Blum et al. 2008. Geology 36:675-678

  8. 5.3 mm/yr 8.4 mm/yr

  9. 1st take home message • Spatial patterns in vertical accretion demonstrate that accretion accelerates in response to subsidence up to a limit. • Beyond some limit, accretion is inadequate to counter submergence (subsidence and global sea-level rise) and marshes convert to shallow open water over several decades. What limits accretion?

  10. Nyman et al. 2006. Estuarine Coastal and Shelf Science 69:370-380.

  11. Nyman et al. 2006. Estuarine Coastal and Shelf Science 69:370-380.

  12. Nyman et al. 2006. Estuarine Coastal and Shelf Science 69:370-380.

  13. 2nd take home message • Now clear that that many marshes, from tidal fresh to saline, from Louisiana to Canada, depend upon organic matter produced by emergent vegetation to vertically accrete. • Roots, rather than stems and leaves, appear to control accretion via vegetative growth.

  14. mineral sediments matter 1. except in the freshest water, only mineral sediments can create suitable conditions in open water for emergent plants

  15. 2. Spartina biomass is positively related to soil Fe and/or mineral sediment density King et al. 1982. Science 218:61-63.

  16. Spartina alterniflora Spartina patens DeLaune and Pezeshki. 1988. Northeast Gulf Science 10:195-204. Nyman et al. 1994. Earth Surface Processes and Landforms 19:69-84.

  17. 3rd take home message • Mineral sediments are needed to create, or recreate, wetlands in open water areas • Mineral sediments probably are important indirectly to marsh vertical accretion via vegetative growth by providing nutrients and moderating sulfide toxicity. • Other factors that can limit plant production probably can limit vertical accretion too; i.e., low nutrient availability, high salinity, too much flooding

  18. Maybe the limiting factor is salinity stress.

  19. Maybe the limiting factor is nutrient availability.

  20. 4th take home message • Marshes receiving more river water have greater aboveground production, and no difference in belowground production than those receiving less river water.

  21. soil organic matter decomposition and marsh vertical accretion

  22. soil organic matter decomposition and marsh vertical accretion 4.1 g N m-2, 4.5 g P m-2 36 g N m-2, 0.5 g P m-2 40 g N/m2, 60 g P/m2, and 40 g K/m2. Fe, Mn, and Zn also were present in trace amounts.

  23. differences appear ecologically significant, although they are statistically insignificant

  24. 5th take home message • Nutrient accumulation and addition rates typically observed in Louisiana had little affect on soil organic matter decomposition rates, but nutrient addition rates typically used in agricultural fields doubled soil organic matter decomposition rates. • Soil near and far from Caernarvon decomposed at similar rates.

  25. stronger soils had less mineral matter McGinnis II, T.E. 1997. Shoreline movement and soil strength in a Louisiana coastal marsh. M.S. Thesis. University of Southwestern Louisiana.

  26. stronger soils had more live roots McGinnis II, T.E. 1997. Shoreline movement and soil strength in a Louisiana coastal marsh. M.S. Thesis. University of Southwestern Louisiana.

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